Arrhythmia is a variation from the normal rhythm of the heart beat and generally represents the end product of abnormal ion-channel structure, number or function. Both atrial arrhythmias and ventricular arrhythmias are known. The major cause of fatalities due to cardiac arrhythmias is the subtype of ventricular arrhythmias known as ventricular fibrillation (VF). Atrial fibrillation (AF) is the most common arrhythmia seen in clinical practice and is a cause of morbidity in many individuals (see e.g., Pritchett, E. L., N. Engl. J. Med. 327(14):1031 Oct. 1, 1992, discussion 1031-2; Kannel and Wolf, Am. Heart J. 123(1):264-7 Jan. 1992). Its prevalence is likely to increase as the population ages and it is estimated that 3-5% of patients over the age of 60 years have AF (see e.g., Kannel et al., N. Engl. J. Med. 306(17):1018-22, 1982; Wolf et al., Stroke 22(8):983-8, 1991). While AF is rarely fatal, it can impair cardiac function and is a major cause of stroke (see e.g., Hinton et al., American Journal of Cardiology 40(4):509-13, 1977; Wolf et al., Archives of Internal Medicine 147(9):1561-4, 1987; Wolf P. A., Abbot R D., Kannel W. B. Stroke. 22(8):983-8, 1991; Cabin R. S., Clubb K. S., Rall C., Perlmutter R A., Feinstein A. R, American Journal of Cardiology 65(16): 1112-6, 1990).
Antiarrhythmic agents have been developed to prevent or alleviate cardiac arrhythmia. PCT Publ. No. WO95/08544 discloses a class of aminocyclohexyl ester compounds as useful for the treatment of arrhythmias. PCT Publ. No. WO93/19056 discloses a class of aminocyclohexyl amides as useful in the treatment of arrhythmia and in the inducement of local anesthesia. PCT Publ. Nos. WO99/50225 and WO04/099137 disclose aminocyclohexyl ether compounds as being useful for the treatment of arrhythmias. PCT Publ. Nos. WO06/138673 and WO06/88525 describe processes for preparing aminocyclohexyl ether compounds. The aminocyclohexyl ether compound, (3R)-1-[(1R,2R)-2-[2-(3,4-dimethoxyphenyl)ethoxy]cyclohexyl]pyrrolidin-3-ol (depicted herein as compound (3)) is an ion channel blocker useful for the treatment of atrial fibrillation (see e.g., U.S. Pat. Nos. 7,057,053, and 7,259,184).
Transaminases, also known as aminotransferases, catalyze the transfer of an amino group, a pair of electrons, and a proton from a primary amine of an amino donor substrate to the carbonyl group (i.e., a keto group) of an amino acceptor molecule. Transaminases have been identified from various organisms, such as Alcaligenes denitrificans, Arthrobacter, Bordetella bronchiseptica, Bordetella parapertussis, Brucella melitensis, Burkholderia malle, Burkholderia pseudomallei, Chromobacterium violaceum, Oceanicola granulosus HTCC2516, Oceanobacter sp. RED65, Oceanospirillum sp. MED92, Pseudomonas putida, Ralstonia solanacearum, Rhizobium meliloti, Rhizobium sp. (strain NGR234), Bacillus thuringensis, Vibrio fluvialis, and Klebsiella pneumoniae (see e.g., Shin et al., 2001, Biosci. Biotechnol, Biochem. 65:1782-1788).
The stereoselectivity of transaminases in the conversion of a ketone to the corresponding amine make these enzymes useful in the asymmetric synthesis of optically pure amines from the corresponding keto compounds (see, e.g., Höhne et al., Biocatalytic Routes to Optically Active Amines,” Chem. Cat. Chem. 1(1):42-51; Zua and Hua, 2009, Biotechnol J. 4(10):1420-31). Transaminases can also be applied to the chiral resolution of racemic amines by exploiting the ability of the transaminases to carry out the reverse reaction in a stereospecific manner, i.e., preferential conversion of one enantiomer to the corresponding ketone, thereby resulting in a mixture enriched in the other enantiomer (see, e.g., Koselewski et al., 2009, Org. Lett. 11(21):4810-2).
Both R-selective and S-selective transaminases are known. The wild-type transaminase from Arthrobacter sp. KNK168 is an R-selective pyridoxal 5′-phosphate (PLP)-dependent enzyme that produces R-amines from some substrates (see e.g., Iwasaki et al., Appl. Microbiol. Biotechnol., 2006, 69: 499-505, U.S. Pat. No. 7,169,592). U.S. application Ser. No. 12/714,397, filed Feb. 26, 2010 and International application PCT/US2010/025685, filed Feb. 26, 2010, disclose engineered transaminase polypeptides derived from the naturally occurring transaminase of Arthrobacter sp. KNK168 that have increased stability to temperature and/or organic solvent, and which have been adapted to have enzymatic activity towards structurally different amino acceptor molecules (see also e.g., Savile, et al., 2010, “Biocatalytic asymmetric synthesis of chiral amines from ketones applied to sitagliptin manufacture,” Science 329(5989): 305-9).
There is a need for improved biocatalysts that can be used to prepare chiral amine intermediate compounds useful for making aminocyclohexylether compounds and new processes employing those biocatalysts that are simple, cost effective, non-hazardous, and commercially viable.